Just
one word: plastics
Perhaps Benjamin Braddock, the confused young man in The
Graduate, ought to reconsider the now-famous pithy advice.
Johns Hopkins engineers have built a battery made of just one
thing: plastics.

Or, to be precise: polymers called poly-fluorophenyl-thiophenes.

Unlike conventional batteries that contain toxic heavy metals
such as lead or nickel-cadmium, or lithium, which is highly
explosive, the polymer battery is non-toxic and safe. What's
more, it's only about as thick as a business card, and malleable
enough to be tucked into existing crevices of a device, thus
eliminating the need for separate battery compartments.

Popular Science recently listed the all-plastic battery
as one of the 100 top scientific developments and inventions for
1996.

"It's lightweight. It's flexible. You can cut it to any shape.
It's made from carbon-based materials, so there are essentially
no environmental concerns," says Peter Searson, professor of
materials science and engineering. And it costs about the same
amount of money to manufacture as a lithium battery, he adds.

The plastic battery, for which a patent is pending, is the
brainstorm of Searson and Theodore Poehler, vice provost for
research, along with post-doctoral students Yosef Gofer and Hari
Sarker, and graduate student Jeffrey Killian, with funding from
the U.S. Air Force. An Air Force-sponsored test and demonstration
of the new device will be conducted aboard a satellite in 1998,
says Poehler.

Searson's group has so far used the batteries to power an alarm
clock and a calculator. They can also be used on other portable
devices such as cellular phones, wristwatches, or hearing aids,
says Searson. Not surprisingly, battery manufacturers have shown
interest in the invention.

The plastic battery's one drawback is its capacity. While it
produces 2.5 volts (enough to be competitive with the 3-volt
lithium batteries now on the market), its capacity is five times
lower. In other words, it needs to be recharged about five times
as often as a comparable lithium battery.

So how can plastic, supposedly an insulator, be used to conduct
electricity? Some plastics, it turns out, are
conductors.

A battery consists of two electrodes--an electron producer called
an anode and an electron acceptor called a cathode--and a
conductive material, the electrolyte. When the Air Force first
asked Hopkins researchers to develop the battery, researchers had
already built batteries containing a plastic cathode, but no one
had been able to find a stable polymer for use as the anode,
explains Searson.

The Hopkins team knew it was in luck last year when it
synthesized a stable polymer suitable for an anode from a class
of plastics called poly-fluorophenylthiophenes. Combined with a
related poly-fluorophenylthiophene serving as cathode, and a
polymer gel electrolyte, the all-plastic battery was born. "To
our knowledge, this is the first all- polymer battery anyone has
made," says Searson. --MH

Contraceptive takes a leap
forward
A new contraceptive gel that appears to prevent sexually
transmitted diseases, as well as pregnancy, is now being tested
in women. The clinical trials, which are sponsored by the
National Institutes of Health, will test whether the gel is safe
and effective.

Hopkins researchers who developed the gel have shown that it
prevents pregnancy in animals, and protects mice against herpes
type II. Their research also suggests that it may prevent
transmission of gonorrhea, HIV, and chlamydia. Biophysics
professor Richard Cone was recently awarded a $2 million grant
from NIH to support further research on the gel.

The contraceptive works by maintaining the vagina's normal
acidity, explains Kevin Whaley, a research scientist in
biophysics and an adjunct faculty member at the School of Hygiene
and Public Health. Normally, the vagina has a ph of 4. All other
things being equal, such acidity would destroy sperm, bacteria,
and viruses. However, semen is alkaline, and raises the vagina's
ph to 7. The "key ingredient" in the contraceptive gel, says
Whaley, is an acidic polymer, which acts like a buffering agent
and keeps the ph at 4.

Sexually transmitted diseases account for five of the 10 most
common diseases reported last year to the Centers for Disease
Control and Prevention, according to a recent report by the
Institute of Medicine (IOM). The IOM reports that in 1994 there
were an estimated 4 million cases of chlamydia, 800,000 cases of
gonorrhea, 101,000 cases of syphilis, between 200,000 and 500,000
cases of genital herpes, more than 1 million cases of pelvic
inflammatory disease, and 79,897 cases of AIDS. --MH

Hot
flashes
A new foil invented by Hopkins engineer Tim Weihs looks like
something you'd wrap around a baking potato. But light a match to
it, and within a second a square-foot section of the foil will
heat up to 2,900 degrees, as a heat-generating reaction occurs.
The fiery exothermic reaction subsides within seconds.

This hot flash ability suggests several engineering applications,
including use as a tough new welding material, says Weihs. A
strip of the new foil can be placed between two objects, and
ignited, forming a tight seal between the two pieces. Because of
its brevity, the blast of heat will not damage the materials.

The foil contains layers of aluminum and another metal such as
nickel, explains Weihs, an assistant professor of materials
science and engineering at Hopkins's Whiting School of
Engineering. Each layer is only 5 to 5,000 atoms thick (1 to
1,000 nanometers), at most.

The foils are made through magnetron sputtering, a technique in
which ions are fired at a target material, knocking off single
atoms that then land on a substrate. By alternating aluminum and
nickel targets, Weihs creates a torte of layered aluminum and
nickel. With co-inventor Troy W. Barbee, a senior research
scientist at Lawrence Livermore National Laboratory in
California, Weihs was recently awarded a U.S. patent for the
foils.

The foil's hot secret is the intimacy between its two types of
atoms, says Weihs. "Certain atoms would rather be bonded to other
types of atoms than to their own kind. Aluminum would rather bond
to nickel than to aluminum, and vice versa." So all it takes is a
"very tiny pulse of heat or friction" to get the bonding started.
Because the atoms are so close to one another, bonding occurs
rapidly, and once the first nickel and aluminum atoms bond, heat
is released, which triggers bonding among neighboring atoms. A
self-propagating reaction ensues.

An added attribute is that the reaction does not require oxygen,
meaning that, technically, the foil does not burn. The new
material could, therefore, be used underwater or in the vacuum of
outerspace, says Weihs. The foil's current high cost (about $60
per six-inch square, a cost that could be considerably reduced,
notes Weihs) may limit its applications to such special uses.
Weihs has also pondered the possibility of using the foils as a
means of burning off cancer cells without harming healthy cells.
--MH

What
lurks beneath the dirt?
Imagine this scenario. The United States is called in to help
fight a war in an isolated region of a foreign country. An
airfield is rapidly constructed by mixing polypropylene fibers
into tilled soil, then packing down the earth. The plastic
reinforces the soil, making it strong enough to support the
weight of helicopters and planes.

This approach has advantages over existing methods for building
temporary airfields, such as laying down interlocking structures
covered by aluminum sheets, says Radoslaw Michalowski, an
associate professor of civil engineering. Aluminum, for example,
which has been used by the U.S. Air Force in the past, is far
heavier and bulkier than plastic fibers.

With funding from the Air Force and the National Science
Foundation, Michalowski developed a theoretical model for
predicting the strength of such soil-fiber composites. His model
has relevance for determining, for example, whether an airfield
composed of the composite will be able to withstand the weight of
a C-130 aircraft.

It all starts in a basement laboratory at the Whiting School.
Open the lab's refrigerator. What's to eat? Yum! A sample of
frozen plastic and dirt--"We like to call it soil," says
Michalowski. Samples such as this one are placed in a sealed
cylinder and subjected to increasing amounts of pressure until--
at some critical point--the mixture collapses. Michalowski's
model predicts that failure point. After testing more than 80
specimens of fiber-laced soil under a variety of conditions, he
says, "The model seems to be very accurate at predicting the
strength or failure of soil."

The fibers belong to a class of materials called "geosynthetics"-
-synthetic materials used to reinforce earth.

In related research, Michalowski is analyzing geosynthetic grids
and fabrics commonly used to reinforce slopes, embankments, and
the soil behind retaining walls.

The engineering of such structures has undergone major changes in
recent years. Retaining walls, which are designed to hold back
dirt where builders have cut into hillsides, have traditionally
been made of concrete that is two- to three-feet thick, says
Michalowski. Floods and earthquakes can total these walls,
turning them into hazardous chunks of concrete. So engineers now
generally reinforce hillside soil with layers of geosynthetic
mesh or fabric. If the synthetics do their job, they prevent
collapse of the hillside and generally do the job of a retaining
wall.

But just the right amount of geosynthetic material must be used,
and it must be placed just so in order to work. If the material
is weak, the soil will collapse. If a length of geosynthetic is
too short, the overlaying soil may slide or roll off. On the
other hand, using more material than is required incurs
unnecessary expense.

Michalowski has created algorithms to determine precisely how
strong a geosynthetic should be, how many layers of the material
should be used, how long each piece should be, and how the
material should be positioned to give the maximum support. So,
for example, given a 50-foot-high slope, with a 40-degree angle
of inclination, Michalowski's formula might predict that 20
layers of a plastic grid should be used, each 50 feet long.

Although geosynthetic materials are extensively used, the public
is not aware of the science that goes into their design--or, for
that matter, that they even exist down there, under the dirt,
says Michalowski.

It's that way with much of civil engineering, he says. Though
feats of civil engineering may not be as scintillating as a super
nova, he says, they have more relevance to everyday life.

So the next time you drive past a retaining wall, think of these
unsung heroes. --MH

Butter your eggs
Despite its sadly tarnished public image, cholesterol has
fascinated biologists and the like for more than 200 years--
mostly because, as it turns out, organisms tend to be more dead
without it. Cell membranes are supple mostly because 10 percent
or so of their structure is cholesterol. It is a major ingredient
in bile, which digests fats. And testosterone, estrogen, and
other steroid hormones necessary to reproduce begin as
cholesterol molecules.

All long established. But now it appears that without
cholesterol we might have never been alive in the first place.

Last fall, Philip Beachy, Jeff Porter, Chin Chiang, and their
colleagues at Hopkins School of Medicine reported in the October
11 Science that cholesterol anchors in place a protein that
orchestrates development in embryos. This new function suggests a
reason why organisms might have evolved this waxy substance in
the first place. Indeed, the more adventurous speculate that
cholesterol could have helped boost primitive, single-celled life
over the evolutionary hump to the wonders of multi-cellular
existence.

Without Hedgehog, the mouse embryo at
right develops a long proboscis and Cyclops-like eye.

Very early in an embryo's life, its notochord (the embryonic
governor) produces a protein called Hedgehog--so named because
without it, fruit flies assume a rounded, bristly shape. In
vertebrates, this dexterous protein signals developing tissue to
form skin, ribs, backbone, and motor neurons, as well as support
cells for the embryonic spinal column. It also rearranges fingers
and toes in their proper sequences.

Hedgehog has two remarkable traits, neither of which, Beachy
discovered, it can accomplish without cholesterol. First, it
activates itself by cleaving in two--but only when a cholesterol
molecule binds to a particular part of the protein and
coordinates the snip.

The cholesterol remains attached to the now-activated half, which
carries the signal to the surface of the cell that made it. What
an unspecialized cell turns into depends upon how much Hedgehog
protein it is exposed to--the second remarkable trait. Cells
adjacent to the notochord get tickled by a lot of Hedgehog and
become support cells, called floor plate. Farther away, cells
receive little protein and so turn into the nerve cells that
control movement. On limbs, a strong signal makes pinky fingers
and a weak one thumbs.

Thus cholesterol's role: Without its cholesterol anchor, the
Hedgehog signal extends farther than it should--presumably
because the protein wanders off. Distant cells are fooled into
forming floor plate instead of motor neurons. Pinkies
proliferate, and so on.

The result then, as Beachy puts it, is "a collection of screw-ups
so severe that fruit flies"--the geneticist's laboratory rat--
"never hatch into larvae." Mice that lack the Hedgehog gene have
a Cyclops-like eye and long proboscis. Human beings may suffer in
a similar way. Children born with Smith-Lemli-Opitz syndrome
(SLOS) cannot make cholesterol: they are missing the final enzyme
in its synthesis. Although their mothers likely contribute
cholesterol in the womb, some of their head and brain
abnormalities resemble those of the Hedgehog-less mice.

How did such fundamental orchestration come about? It's logical
that early, single-celled life used some sort of signals to
recognize each other and mate, for example. Over time, organisms
could have evolved these primitive nametags into signals to
customize cells for specific tasks. And a key step in
customizing, or cell differentiation, would be getting the proper
signal to its proper place. Enter cholesterol.

That scenario may end up less fantastic than one might think,
says Beachy. Eugene Koonin of the National Library of Medicine
recently called his attention to a coincidence. Koonin, a
geneticist, had noticed that the part of Hedgehog where
cholesterol forms its bridge bears a remarkable resemblance to
part of something recognized less than 10 years ago:
self-splicing proteins.

"Self-splicing proteins may be nature's tidiest parasites," says
Beachy. These proteins get a host cell to replicate them by
quietly inserting their DNA into specific places along genes. The
cell's own machinery manufactures the parasite along with the
real product. Then the self-splicing protein just as quietly cuts
itself out, neatly reties the ends of its host protein, and goes
on its way, the host unharmed.

The sequence that Koonin saw in common was where one end of
splicer meets host, and where the cleaving part of Hedgehog joins
the signaling part. Is this an evolutionary coincidence, or did
an enzyme in cholesterol metabolism have some ancient
entanglement with the machinery of a self-splicing protein?

Another coincidence shows up with Hedgehog's three-dimensional,
structure. Nestled within its protein chain are a zinc atom and a
water molecule. They are arranged in a tetrahedral shape that
Hedgehog turns out to share with an enzyme in soil bacteria
called Streptomyces (from which come several antibiotics). This
enzyme uses the zinc-water complex to prevent formation of
cross-supports between the sugar chains of cell walls. Could
Hedgehog, closely associated with cell membranes, have inherited
the complex from this enzyme? Perhaps the protein sometimes needs
to free itself from its cholesterol anchor, or to move in some
other fashion through tissues. Speculation to be sure, says
Beachy: "There may well be aspects of Hedgehog signaling that we
haven't discovered yet."

There are signs that cholesterol may help process more proteins
than Hedgehog. Porter and Keith Young checked their work in
Beachy's lab by feeding a kidney-cell culture with radio-labeled
cholesterol. Hedgehog lit up, as expected--but so did several
other proteins. They are as yet unidentified.

"This is very preliminary," warns Porter, "but we may be dealing
with a fundamental process in development that no one has ever
seen before."